The genome of SV40 has provided one of the most effective tools in cell and molecular for the analysis of eukaryotic gene expression and oncogenic cell transformation. Depending on the type of cell, the introduction of viral DNA either subverts the host into replicating the viral genome to high copy numbers or alters its properties of growth and tumorigenicity. The mechanisms by which the small genome of SV40 can effect these processes will be studied using a variety of approaches that will involve collaborative interactions between four laboratories. These will include: analysis of the influence of mutant and wild type viral oncogenes on the growth properties of primary and established human cells; utilization of in vitro systems and enzymological approaches to characterize the means by which the viral oncogenes are generated by alternative RNA splicing; charcterization of the interaction of the viral tumor antigens with host cell components; as well as probing the structures of important regions of the viral DNA molecule using a novel set of reagents.